Regulating conductor for electric heaters



v I 1,510,125 Sept 30 1924' w. H. WOODFORD REGULATING CONDUCTOR FOR ELECTRIC HEATERS Original i e g- 11, 1 920 I A A I JIATTS CONSUMED AT VARIOUS TEMPERATURES IN A GCMPOSITE CONDUCTOR FORMED OF our: STRAND OF HIGH RESISTANCE ALLOY WIRE AND ONE STRAND O1? IRON WIRE.

RESISTANCE AT VARIOUS TEMPERATURES OF A HIGH RESISTANCE ALLOY WIRE- RESISTANCE AT VARIOUS TEMPERATURES OF 1m mow WIRE.-

flslsmncz AT VARIOUS TEMPER- ATURES OF A COMPOSITE WIRE.

0 F. zoor. 400 F. 600' F. 800' F. 1000 F. 1200 F.

. TEMPERATURE WA T'X'S OHMS -WITNE$5 Ti 5 INVENTOR M 74/. KM. WATSON H.. WOODFQRZD.

Fkuww ATTORNEY Patented Sept. 30, 1924.

v UNITED STATES PATENT OFFICE.

WATSON WOODFORD, OF BRIDGEPORT, CONNECTICUT.

R EGULATING CONDUCTOR FOR-ELECTRIC HEATERS.

Application filed August 11, 1920, Serial No. 402,756. Renewed January 23, 1924.

To all 10/2 am it may concern: I

Be it known that I, lVA'rsoN H. VVooDronn, a citizen of the United States, residing at Bridgeport, in the county of Fairfield and State of Connecticut, have invented certain new and useful Improvements in Regulating Conductors for Electric Heaters, of which the following is a specification.

This invention relates to electric heaters such as electric irons, soldering irons. water and room heaters, utensils, etc., and has for an object the provision of an improved conductor for such devices. A further object is to provide a conductor so constructed that the heat developed decreases with increase in temperature, whereby'the heater is rapidly brought up to working temperature and this temperature is then automatically maintained. 1 Other objects and advantages will appear ater.

Fig. 1 shows a section of conductor illustrating the invention and Fig. '2 shows graphicallythe characteristics of the conductor of the present invention as compared with the characteristics of other conductors.

It is desirable to so construct electric heaters that the resistance is relatively low at low temperatures but considerably higher at high temperatures. Such heaters will quickly come. up to working'temperature and will be automatically maintained at this temperature on account of the regulating effect of the conductor.

It has been proposed heretofore to secure this result by employing a heating conductor of iron which has a very high positive resistance temperature coeflicient. These attempts were apparently unsuccessful because not enough space is available in such electrically heated devices to permit of the use .of a sufficient length of the proper sized wire; this for the reason that the resistance of iron is quite low and its permissible working temperature is likewise low. Such high resistance alloys as nickel-steel, nickelohromium, etc., have a negligible temperature coefiicient and therefore cannot be used for regulation. In an application for United 5 perature coefficient. Such a conductor will States Patent S. N. 402,276, filed August.

have suflicie'nt regulating effect while also furnishing suiiicient resistance to enable it to be used in the small space available.

After considerable experiment it has been discovered that an excellent conductor for this purpose can be made by using a high resistance conductor having a negligible temperature coeflicient in parallel with a conductor having a high positive temperature coefiicient such as iron. In the drawing the letter A indicates a high resistance conduc- I tor of any suitable material-such as an alloy of nickel and steel or nickel and chromium or other alloy, while the letter B indicates a conductor having a high positive co efficient such as iron. While these conductors may be kept insulated with respect from each other, it has been found satisfactory to twist the conductors one upon the other. As a greater length of iron wire is usually needed the iron Wire may be coiled upon the alloy wire as shown. A though this would seem to'make the two conductors in effect a single conductor it has been found that they obey the well-known laws of shunt circuits. This is probably due to the fact that the electrical potential between the two conductors at any point is negligible, particularly when the pitch of the coil is constant throughout its length. Referring to Fig. 2 the curve R indicates graphically the change of resistance of a conductor of high resistance -material as the conductor A through a temperature range of from about 75 Fahr. to 1200 F ahr. it will be seen that the resistance increases somewhat with temperature but that this effect is quite negligible, amounting to only about 45% over the entire range. The curve R shows the change of resistance of an iron wire over the same temperature range amounting to about 650%. The curve R illustrates the change of resistance over the same temperature range of a conductor made according to the present invention and consisting of the conductors A and B in parallel. The dimensions of the conductors havebeen so chosen that their resistance at normal temperatures is the same, as is apparent from the curves. The increase in resistance is about 360%. It is less than that of iron taken alone but greatly in excess of the re sistance increase of the alloy taken alone. This increase has been found quite sufiicient for regulating purposesiand not So excessive From this as to cause too large a current flow when the heater is cold.

The curve W shows the variation in watts consumed by the composite conductor at various temperatures, showing a rapid 'decrease in higher temperature.

An important advantage inherent in this construction is the fact that the conductor is continuous and it is not necessary to form joints in the conductor within the heater.

Such joints are difiicult to make and fre-- quently cause short circuits and other troubles in the use of the heater A further advantage is that this composite conductor can be made up in any quantity and later cut ofi' in suitable lengths to be incorporated into the heater. By coiling the one upon the other, as-shown, the proprtionate length and thickness of the wires can be varied to suit requirements. However, when once wound the proportion of the lengths of the two types of conductor is fixed and will be the same for any length. Thus it will be a simple matter to provide each heater with just the.

has been found tohave many advantages it is to be noted that other ways of carry ing out the invention may be employed and these are intended to be comprehended within the meaning and range-of equivalency of the following claims 1. A heating conductor for electric heaters comprising a high resistance conductor having a low resistance temperature co'efiicient and a conductor in parallel therewith having a high positive' resistance temperature coefiicient.

2. A heating conductor for electric irons comprising a high resistance conductor having a low resistance temperature coefiicient and an iron conductor in parallel therewith.

3. A heating-conductor for electric heaters comprising a nickel steel conductor and a conductor in parallel therewith having a high positive resistance temperature coeflicient.

4. A heating conductor for electric heaters comprising a nickel steel conductor and an iron conductor in parallel -therewith.

5. A heating conductor for electric heaters comprising a high resistanceconductor having a low resistance temperature vcoeiiicient and a conductor in parallel therewith having a high positive resistance temperature coefficient, one of said conductors being coiled upon the other.

6. A heating conductor for electric heaters comprising a high resistance conductor having a low resistance temperature coefiicient and a conductor in parallel therewith having a high positive resistance temperature coeflicient said last-named conductor being coiled upon the first named conductor.

7. A heating conductor for electric heaters comprising a high resistance conductor having a low resistance temperature coeflicient and a conductor in parallel therewith having a high positive resistance temperature coefiicient, one of said conductors being coiled upon the other, the pitch of said coil being constant.

8. .A heating conductor for electric heaters comprising a high resistance conductor having a low resistance temperature coeflicient and a conductor in paraliel therewith having a high positive resistance temperature coeflicient said last named conductor being coiled upon the first named conductor, the pitch of said coil being constant.

In witness whereof I have signed my name hereto this 6 day of Au 1920.

WATSON 1- WOQDFORD. 

